This invention relates to an extruding die for forming finned honeycomb structures by extruding.
Ceramic honeycomb structures have been widely used for catalyzer carriers for purifying exhaust gases from internal combustion engines, filters for removing fine particles in the exhaust gases and heat exchange elements for the exhaust gases, because the ceramic honeycomb structures are superior in heat resistance and corrosive resistance and have wide surfaces contacting combustion gases with less pressure losses.
In general, the ceramic honeycomb structures are manufactured by the forming method with extruding dies.
An extruding die for this purpose has been known from, for example, Japanese Patent Application Publication No. 61,592/82 whose die is provided with tapered portions between honeycomb forming grooves and extruding supply apertures for forming raw material into a honeycomb structure. Another extruding die has been known from Japanese Patent Application Publication No. 1,232/76, wherein a solid block is provided with first and second channels, and supplied material is extruded from the first channels to the second channels to form a module. Moreover, a further die has been known from Japanese Laid-open Patent Application No. 54-8,661, wherein a feed hole member and an extruding slot member are formed with feed holes and extruding slots, respectively and small apertures are provided therebetween. Furthermore, U.S. Pat. No. 3,038,201 disclosed a die which comprises forming material supply apertures into which a ceramic material is first supplied from an extruder, grid-shaped forming slots and pooling areas between the supply apertures and the forming slots for temporarily accumulating the ceramic material therein.
With all these extruding dies, the supply apertures for the ceramic material are opened at intersections of the extruding slots and communicated therewith, and only partition walls of honeycomb structures are formed by the ceramic material supplied into the supply apertures. A die for forming finned ceramic honeycomb structures has not been known yet.
In recent years, attempt has been made to enlarge surface areas per unit volumes of the ceramic honeycomb structures in order to improve the purifying performance of catalyzer and filtering performance.
For this purpose, a finned ceramic honeycomb structure (Japanese Patent Application No. 7,362/85) has been proposed. The inventors of the present application attempted to produce the proposed finned ceramic honeycomb structure by applying the above described extruding dies of the prior art.
In the case where finned ceramic honeycomb structures are formed by the use of the extruding dies of the prior art, fins branched from partition walls forming the honeycomb structures are uneven in height and width and even if formed fins are sound in appearance, they are uneven in density so that cracks would occur when drying or firing the honeycomb structures.
With the extruding dies for producing finned ceramic honeycomb structures, moreover, it is necessary to inspect whether branched forming grooves provided in surfaces of the dies on outlet sides for ceramic materials have been formed with required accuracy in dimension without any damage. Such an inspection is a troublesome and time-consuming operation.
The inventors of the present application have investigated the problems arising in forming finned ceramic honeycomb structure by means of the extruding dies of the prior art and ascertained that the problems result from the fact that with the dies of the prior art only formed with branched forming grooves for fins, the relation between ceramic material supply holes and branched forming grooves for forming the fins is indefinite and therefore the ceramic material is not supplied into the branched forming grooves sufficiently to form complete fins although the material is uniformly supplied to form the partitions of honeycomb structures.